Electrode structure



July 12, 1960 G. F. MARX 2,945,152

ELECTRODE STRUCTURE Filed May 22, 1959 2 Sheets-Sheet 1 FIG. FIG. 5

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(PRIOR ART) INVENTOR: GEORG F. MARX PATENT 4 7 July 12, 19 e. F. MARX 2,945,152

ELECTRODE STRUCTURE Filed May 22, 1959 2 Sheets-Sheet 2 INVENTOR:

' GEORG F. MARX 4 BY gm PATENT AGE/V r- ELECTRODE STRUCTURE Georg F. Marx, Ulm (Danube), Germany, assignor to Telefunken G.m.b.H., Berlin, Germany Filed May 22, 1959, Ser. No. 815,225

Claims priority, application Germany May 22, 1958 1 Claim. (01.313-350) The present invention relates to a tensioned grid for electrical discharge tubes, particularly for electronic tubes, and further relates to an electrode assembly forsuch tubes having one or more such tensioned grids.

For several reasons, it is desirable to very closely space electrodes in electrical discharge tubes, especially in tubes used for very high'frequencies.

the cathode surface to a minimum when the known tensioned grids are used. However, if such grids are employed, it is diflicult to reduce the distance between the individual grids below a certain minimum, as for in stance the distance between the control grid and the screen grid, or the distance between the control grid and the anode. This is due to the presence of bows or spacers which are necessary in tensioned grids for maintaining the separation between the supporting wires on which the grid is wound.

Minimal spacings between the control grid and the screen grid are, for example, necessary if sufficiently high grid penetration factors are to be obtained at low screen grid voltages and/or anode voltages with fine-mesh control grids. By applying low screen grid and/or anode voltages, the life of such tubes is increased and the total power loss is reduced. As an immediate result of lower voltages, for instance, in multiple grid tubes, superior current distribution and a more favorable static noise factor are obtained, because thinner screen grid wires can then be used.

It is an object of the present invention to provide a tensioned grid design which makes it possible to reduce the spacing between the control grid and the screen grid, or between the control grid and the anode, to a minimum in order to realize the above-mentioned advantages. A tension grid is to be used comprising wires supporting the grid turns and having spacer bows maintaining the separation of the wires.

It is another object of the invention to replace at least one of the prior-art spacers interconnecting the grid supporting wires by a metal bridge which is disposed in the common plane of the supporting wires and is connected to the outer ends thereof, said metal bridge being no wider than the thickness of the supporting wires.

The advantage of the inventive tension-grid design resides in that the bridge lying in the central plane during mounting of the next outer electrode, for example, the screen grid or the anode, does not obstruct the mounting so that the next electrode can have a minimum distance from the first-mentioned grid.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this, detailed description.

It is possible to v reduce'the distance between the first control grid and 2,945,152 Patented July 12, 1960 In the drawing:

Figure 1 shows a sectional view of a prior-art tension grid structure.

Figure 2 illustrates a front view of the grid structure in Figure 1.

' Figures 3 and 4 show corresponding views of a tension grid structure according to the invention, in end and front view, respectively.

Figure 5 is a front view partly in section showing the invention applied to a tube having a screen grid.

Figure 6 is an end view of the grid structure shown in Figure 5.

The difference between the tension grid according to the invention and the known structures of tension grids may be readily recognized by comparing the prior-art design of Figures 1 and 2 with that of an embodiment of the invention according to Figures 3 and 4.

In Figures 1 and 2, the prior-art grid comprises two supporting wires 2 and 3 which are joined to form a frame by means of two bows. 4 and 9. These two bows 4 and 9 are suitably secured to the supporting wires 2 and :3 by spot-welding. Grid turns 8 are then wound on the Wires 2. and 3 using a mechanically tensioned grid wire. The bows 4 and 9 have the form shown in Figure l to permit insertion of the cathode 1 between the grid turns 8 during assembling of the system.

As can be seen from Figure 1, a next outer grid 7, supported on members or wires 5 and 6 has to be spaced from the grid turns 8 of the first grid by the distance occupied by the bows 4 and 9, because otherwise the outer grid 7 cannot be placed over the first or inner grid 8 during assembling. Therefore, bows 4 and 9 should occupy the least possible distance between the two superimposed grids. 1

In the inventive construction, shown in Figures 3 and 4, one of the bows is replaced by a bridge-like spacer member 10 lying in the central plane between the two supporting wires 2 and 3 and attached to the ends of these two wires2 and 3. Figure 3 clearly shows that the spacing between the grid turns 8 of the first or inner grid and the turns 7 of the second or outer grid is substantially reduced to provide the advantages described above.

In accordance with the invention, a tension grid, as shown in Figures 3 and 4, is to be used in an electrode assembly in which the electrodes or their support means are attached between plates of insulating material. In contrast to the known constructions of an electrode assembly, the embodiment shown in Figures 5 and 6 provides on one end two plates of insulating material, one of these plates 13 having a cutout corresponding to the grid profile, while the other plate 12 is made of two parts and serves primarily to mount the cathode. During assembly of a tension-grid structure according to this embodiment of the invention, the individual electrodes are inserted in cutouts or openings provided therefor in an insulated plate 11, i.e., the cathode 1 with its heater, the control grid with two supporting Wires 2 and 3, the screen grid with two supporting wires 5 and 6, and then the other electrodes of the system. Due to the design of the control grid and, particularly, of the bridge-like spacer member 10, explained with reference to Figure 4, it is possible to assemble the screen grid over the control grid, i.e., insert the screen grid into respective recesses of the plate '11, even if the mutual spacing of these two grids is extremely small.

A plate 13 of insulating material is first applied to the outer ends of the electrodes or the supports carrying the electrodes, said plate having a cutout 16 corresponding to the cross section of the control grid. With the exception of the cathode 1, all of the electrodes of the structure are aligned by means of this plate 13. A second ,3 plate 12 of insulating material is provided to secure the cathode, said plate being divided in the plane of the supports 5, 2, 3, 6,so that it can be assembled despite the presence of the bridge member 10, and this plate, being provided with cutouts receiving these supports andthe cathode 1-. The two halves of this plate 12 are assembled in such a way that the two plates 12 and 13 engage one another. Thus, all of the electrodes, including the cathode, are mounted and the structure in which the cathode and the control grid, as well as the control grid and the screen grid, are spaced can be assembled in the tube envelope. Means are provided to. fix the two plates 12 and 13 in their positions with respect to each other, for example, by means. of the supporting means or wires 14 and 15, shown in Figures 5 and 6. 7

It is to be noted that the electrode design shown in Figures 5 and 6' is regarded only as an example, because other mounting means may be used for the cathode than the divided plate 12 of insulating material.

Furthermore, in a tube having more than two grids, additional grids, for example a suppressor grid, may be provided in accordancewith the invention so that in this manner a tube assembly with extremely small electrode spacings. may be obtained. a

What is claimed is: V a 7 An electrode assembly for an electrical discharge tube, said assembly comprising a tension grid structure having supporting wires, tensioned grid wire turns wound on the supporting wires, and spacer means maintaining the separation between the supporting wires, at least one of said spacer means comprising a spacer member disposed in the common plane of the supporting wires and extending therebetween, said spacer member being fixed at its ends to said supporting wires and being of a thickness no greater than the thickness thereof; said assembly further comprising other electrodes including a cathode; said assembly still further comprising inner and outer spaced insulated plates; the electrodes, the cathode and grid supporting wires being mounted at their inner ends in one plate, and said plates at the outer end comprising two plates of insulating material, one of said plates having a cutout corresponding to the grid structure profile adjacent said spacer member, and the other of said plates being divided into two parts and having cutouts exactly fitting the electrode supports and serving primarily to secure the outer'end of the cathode.

1,721,405 I Mullaney 3 July 16, 1929 1,865,715 Krahl July 12, 1 932 

